Anatomy of an engine: Heart condition

The four-stroke engine was first patented nearly 150 years ago, and a lot has changed since then. We attempt to explain what happens to your fuel when modern engines get to work.

So, you’ve filled up with our fast acting performance fuel Shell V-Power Nitro+ Unleaded, designed to get to work instantly in your engine. But what’s happening in there? How does it all work?

It’s all about control. The four-stroke cycle working the engine is basically the same as it’s been for the last 100 years. However, the detail is very different. Today it’s all about getting as much energy out of as little fuel as possible.

So what exactly are the innovations that make today’s four-stroke petrol engine so advanced?

Variable Valve Timing

In the past the inlet and exhaust valves opened and closed at set times, dictating the engine’s characteristics and performance. But if you alter when the valves open and shut, you’ll get an engine capable of high speeds that doesn’t compromise on low-speed pulling ability.

Variable valve timing is achieved by altering the rotational position of the inlet camshaft relative to the exhaust camshaft.

Valvematic, Valvetronic, MultiAir & more

Next, we change how much, and for how long, the valves stay open. The best way to alter the amount and duration of opening is to do it continuously over a wide range.

A throttle is unnecessary. Instead, if you use the inlet valves to control airflow, by altering how far they open, this removes a major obstruction to airflow.

Carmakers had spent years trying to design systems that can open the valve electronically or hydraulically, free from the camshaft’s limits. They eventually achieved this goal in 2009, creating the MultiAir engine that could pull energetically from low speeds and rev like a racing car without compromising on performance.

Now comes the clever part: an electric solenoid valve bleeds off part of the oil flow in the hydraulic pipe as required, up to 60 times a second, leaving the rest to open the inlet valve. It’s probably the most significant breakthrough in piston engine design in the last 100 years.

Direct Injection

With direct injection, the fuel is squirted straight into the cylinder. Under light load, it can be squirted just before the spark occurs, near the top of the compression stroke. Essentially, you can inject less fuel than the total volume of air theoretically needs and still get a proper burn.

For high-power running, the fuel is injected on the induction stroke as with indirect injection. This gives time for more fuel to be injected, cooling the air as it enters the cylinder. This means the mixture can be compressed more without overheating.

Turbocharging

A turbocharger has a turbine that uses waste energy from the flow of exhaust gases to drive an air compressor - it’s as close to a free power boost as you’ll get. The turbo compresses the air and forces it into the engine, so more can be squeezed into each cylinder for increased power.

Protect it with Shell

The technology we’ve mentioned so far is all to do with managing the four-stroke cycle, but there are many more ways in which modern engines save energy. Friction is the enemy of efficiency, so the easier an engine’s components can move, the better.

Shell oil not only lubricates the engine but also cleans it of harmful deposits thanks to ingenious active cleansing agents. You can check which oil offers your engine the optimum protection using the Shell lube match tool.

The strokes in four simple steps

Step one

Let’s get to grips with how a conventional port fuel injection four-stroke petrol engine works.

1. The inlet valve opens as the piston is about to descend, sucking in the mixture of fuel and air.

Step two

2. With both valves now closed, the piston rises upwards, squeezing the mix of fuel and air.

Step three

3. Just before the piston reaches the top, the fuel and air mix is ignited by the spark plug.

Step four

4. The exhaust valve opens and the piston rises back to the top, expelling the burnt gases.